In a filament type trimmer having a filament storage spool mounted in a rotating housing having a rim portion with an exit aperture through which the filament extends, frequent breakage of the filament has been found to occur where the filament exits from the cutting head. It has been determined that the exit aperture has no effect on filament breakage so long as the filament is rotating in free air and does not strike any relatively stationary object. Thus any suitable means for allowing the string to pass through the outer wall of the housing is suitable under these conditions. However, when the cutting filament hits a relatively stationary object, the filament is deflected rearwardly and a component of the impact load is transmitted along the filament. This tensile load causes the filament to stretch and, moreover, applies a high localized load where the filament bends at the exit aperture.
It has been proposed to support the filament by a substantially curvilinear bearing surface at the exit aperture and to form the bearing surface of a material having a low coefficient of friction with respect to the filament. While these expedients have been found to be somewhat beneficial in reducing filament breakage, it has been found that they do not provide a complete solution to the problem.